In the U.S. patent application, Ser. No. 568,940, filed 1/9/84, now U.S. Pat. No. 4,536,532, it has been disclosed that polyvinyl alcohol homopolymer can be made melt extrudable by the addition of certain organic, non-hydroxylic plasticizers, selected from the class of aromatic sulfonamides, aromatic sulfonates, aromatic phosphates, aromatic phosphites, alkylene carbonates, alkyl pyrrolidones, dimethyl amides of fatty acids, and admixtures thereof. These compositions exhibit a significant oxygen barrier to oxygen, even at elevated humidities.
In U.S. Pat. No. 3,607,812 Takigawa discloses the melt extrusion of a conventional polyvinyl alcohol with the use of glycerine in a water-free environment, where the polyvinyl alcohol utilized has a degree of hydrolysis of 97% and a degree of polymerization of 700-1500.
In U.S. Pat. No. 4,451,438 Knott and Odorzynski have used substantial amounts of polyethyl oxazoline, polyvinyl pyrrolidone, polyvinyl formaldehyde and polyamides having melting point temperatures below 400 degrees F. as blends with the copolymer of ethylene/vinyl alcohol to affect easier processing. They note only that the oxygen permeability of such blends, using between 5 and 20% by weight of plasticizing polymer, does not rise above 1 cc/square meter/24 hrs. at 0% humidity and 73 degrees F. Their information does not disclose any permeability values for gases.
In U.S. Pat. No. 4,464,438, Lu describes blends of polyvinyl alcohol and ethylene/vinyl alcohol copolymer with the use of processing aids, such as polyamide, polyurethane or polyoxazoline for producing opaque, paper-like films. There is not mention of improvement in impermeability properties with the use of these processing aids, in the range 5-20%.
In U.S. Pat. No. 3,516,960, are given various benzoate esters, including salicylate esters, that provide some improvement in oxygen permeability. However, these materials are all monomeric and they are used in water cast films, rather than melt extrudable systems.
In U.S. Pat. No, 4,284,671, are provided data on the oxygen permeability benefits of adding polyester copolymer to ethylene/vinyl alcohol copolymer. No change in oxygen permeability is perceived until the copolyester concentration reaches 25% by weight, and preferably near 50%, in order to provide a composition with impermeability to oxygen approaching ethylene/vinyl alcohol copolymer.
In U.S. Pat. No. 4,289,830 is disclosed the use of small amounts of phenolic monomers for improvement in oxygen permeability, with the best increase in protection being 42% of the ethylene/vinyl alcohol copolymer. The values cited are very high in light of other literature references for ethylene/vinyl alcohol copolymer.
In U.S. Pat. No. 4,003,963 are disclosed blends of vinyl chloride polymers with ethylene/vinyl alcohol copolymer in the amount of 10-30 percent, in conjunction with carboxyl moieties in the PVC.
All of the cited references use monomeric additives or use large amounts of polymers cited to have effects that are diluent on the impermeability of polyvinyl alcohol polymers and copolymers to oxygen gas. This invention relates the significant improvement in already high barrier compositions to oxygen permeability by the addition of only small amounts of selected polymers in the range 0.5% to 4.5%. The low impermeabilities of melt extrudable polyvinyl alcohol compositions are further reduced with the addition of Nylon 6, 66, and poly(butylene terephthalate).